Apparatus for the automatic control of electric motors



Jan. 10, 1956 A. OBERMOSER APPARATUS FOR THE AUTOMATIC CONTROL OF ELECTRIC MOTORS Filed Jan. 14, 1953 ALBERT OBERMOS ER 2 Sheets-Sheet l Jan. 10, 1956 A. OBERMOSER 2,730,585

APPARATUS FOR THE AUTOMATIC CONTROL OF ELECTRIC MOTORS Filed Jan. 14. 1953 2 Sheets-Sheet 2 INVENTOP: Aman- OBERPMSER BX United States Patent O APPARATUS FOR THE AUTOMATIC CONTROL OF ELECTRIC MOTORS Albert Obermoser, Miesbach, Germany Application January 14, 1953, Serial No. 331,128

Claims priority, application Germany January 15, 1952 3 Claims. (Cl. 200-47) This invention relates to an apparatus for the automatic control of electric motors.

It is an object of the invention to provide means by which the motor can be automatically controlled, more particularly its direction of rotation can be reversed, in dependence upon the feed of a tool, for instance the depth of a bore or the length of a female thread produced in a bore hole.

A special object of the invention is to automatically reverse the direction of rotation of a screw tap when its cutting action has been completed and again when a new hole is to be tapped.

With this and other objects in view, this invention consists in the details of construction, combination of elements and operation hereinafter set forth and then specifically designated by the claims.

In order that those skilled in the art to which this invention appertains may understand how to make and use the same, I will describe its construction in detail, referring by numerals to the accompanying drawings forming part of this application, in which:

Fig. 1 is a front view of the automatic switch apparatus having the invention applied thereto, with the cover removed,

Fig. 2 is a side view thereof, partly in section, showing the parts in a position before the beginning of the cutting operation of the tool,

Fig. 3 is a similar view, but showing the parts upon termination of the cutting operation, and

Fig. 4 is a fragmentary plan view, with the cover of the casing attached.

Similar reference numerals denote similar parts in the different views.

Referring to the drawings in greater detail, it will be seen that knife edge bearings 4 and 5 are arranged at different heights on the rear wall 1 of a casing 2 which is connected to a motor 3 by flange connection. A see-saw lever 6 is mounted in the knife-edge bearing 4 in such a way that it is able to swing perpendicularly to the plane of the drawing of Fig. 1. Similarly, the lower edges of a pair of legs 7 of a see-saw lever S are supported in the two lower knife-edge bearings 5. The see-saw levers 6 and 8 may consist of metal or of an insulating material and are tensioned towards each other by a pair of helical tension springs 9 being under preliminary tension, so that their bearing edges are urged into the knife-edge bearings 4, or 5, resp. In the position of Fig. 2 an extension 10 of the see-saw lever 6 forms the abutment for the see-saw lever 8. The upper edge of the last-mentioned see-saw lever engages in a notch 11 of a see-saw lever 13 fulcrumed in the casing at 12 and carrying a pair of mercury switches 14. The casing 2 is provided with two eyes 15 for fixing the cover of the casing 16 and with two further eyes 17 serving to guide pins 18. The pins 18 bear at their free ends a contact plate or striker 19 serving to engage the workpiece 20. The contact plate 19 is acted upon by helical springs 21 surrounding the pins 18 and lying against the cover 16 of the casing at 22, thus tendopening 25 and through a recess 26 of the see-saw lever 6. e

A stop 29 is provided at the end of the feeler bar 24, while an adjustable stop member 31 is shiftable on the feeler bar 24 in front of the see-saw lever 6 and can be fixed in position by means of a screw 39. The motor shaft 32 is passed through the casing 2 and its cover 16 and bears at its end a screw tap 33. The contact plate 19 is perforated to allow passage of the screw tap. In the initial position only the tip of the tap projects from the contact plate 19, so as to find its way into the bore of the workpiece for threading the same.

The operation of the apparatus is as follows:

The workpiece 26 is engaged with the contact plate 19, i. e., in such a position that when closing the circuit of the electric motor through the main switch (not shown) the cutting edge of the screw tap 33 engages the workpiece 20 exactly in the bore thereof and the tap cuts a thread into the workpiece by its being advanced in an axial direction, until the stop 31 secured on bar 24 swings the seesaw lever 6 beyond the dead centre position, whereby the mercury switch 14 is tipped, through the see-saw system 8, and the tap is turned out of the bore of the workpiece, owing to the reversal of its direction of rotation, assisted by the relaxing springs 21. As a result, the feeler bar 24 is also returned to its initial position, in which the-stop 29 at the end of the feeler bar takes the see-saw lever 6 back to its initial position, so that the system 6, 8 springs again from the position of Fig. 3 into that of Fig. 2, whereby the motor is again reversed, by tipping reversal of the mercury switches 1 and prepared for tapping the next workpiece.

While the invention has been described in detail with respect to a now preferred example and embodiment of the invention it will be understood by those skilled in the art after understanding the invention that various changes and modifications may be made without departing from the spirit and scope of the invention and it is intended, therefore, to cover all such changes and modifications in the appended claims.

I claim:

1. An apparatus for automatically controlling an electric motor in dependence upon the feed of a threading tool driven by said motor, comprising a casing adapted to be engaged with the non-rotating driving means of the threading tool, a quick-break switch system accommodated in said casing and comprising two see-saw levers and associated knife-edge bearings for said levers, tension spring means whose opposite ends are suspended from the two levers whereby the levers are drawn together and held in their knife-edge bearings, a mercury switch system controlled by the first of said levers in such a way that the two extreme positions of the mercury switch system correspond to the two operative positions of the switch for reversal of the direction of rotation of the motor to be controlled by the switch, a contact member adapted for engagement with the workpiece, means for slidably guiding the contact member in relation to said casing and spacing it therefrom under spring action, and a rod for transmitting the relative movements of the contact member to the second of said levers, whereby the levers are caused to spring into their opposite end positions, through the dead centre position, as the respective end position of the contact member has been reached, for reversing the mercury switch.

2. An apparatus for automatically controlling an electric motor in dependence upon the feed of a threading tool which is driven by said motor, comprising a casing adapted to be engaged with the non-rotating driving means of the threading tool, a quick-break switch system accommodated in said casing and comprising two seesaw levers and associated knife-edge bearings for said levers, tension spring means whose opposite ends are suspended from the two levers whereby the levers are drawn together and held in their knife-edge bearings, a mercury switch system controlled by the first of said levers in such a way that the two extreme positions of the mercury switch correspond to the two operative positions of the switch for reversal of the direction of rotation of the motor to be controlled by the switch, a contact member adapted for engagement with the workpiece, means for slidably guiding the contact member in relation to said casing and spacing it therefrom under spring action, said casing and said contact member having a throughbore for passage therethrough of the rotary carrier of the threading tool, a rod and an adjustable stop on said rod for transmitting the relative movements of the contact member to the second of said levers, whereby the levers are caused to spring into their opposite end positions, through the dead centre position, as the respective end position of the contact member has been reached, for reversing the mercury switch.

3. In an arrangement for working a workpiece member by a tool member comprising, in combination, supporting means; electric motor driving means alternatively rotatable in one direction and an opposite direction thereto; snap-action switch means associated with said driving means and movable between two positions in one of which it operates said driving means in said one direction and in the other of which it operates said driving means in said opposite direction, said snap-action switch means including a mercury switch movable to different positions for operating said electric motor driving means in opposite directions, a pair of levers resiliently connected to each other and knife-edge bearings on which said pair of levers are resiliently held, one of said levers engaging said mercury switch for moving the same; holding means movably mounted on said supporting means for holding one of said members and connected to said driving means so as to be driven by the same in one of said directions determined by the position of said switch means; actuating means movable relative to said supporting means between a retracted and an extended position for moving said switch means from one of said positions thereof into the other and back, said actuating means having a contact portion extending and being located in the region of the member held by said holding means so as to be adapted to he in permanent contact with the other member during working and be operated by the relative movement of said other member relative to said one member held by said holding means, and having a switch engaging portion movable with said contact portion for engaging and actuating the other of said levers of said switch means upon movement of said actuating means between its retracted and extended positions; and resilient means constantly urging said actuating means toward its extended position.

Schildknecht June 6, 1950 Johnson July 21, 1953 

